The present invention relates to a display device substrate to be used in the production of panels for display devices, particularly liquid crystal display devices and organic EL devices. More particularly, the present invention relates to a display device substrate which is lighter in weight and less liable to break than the conventional one.
The recent rapid development in computer networks and digital communications has involved an even larger number of personal users in the advanced information society having information networks as one of its bases, and it has created the need for diversification and sophistication, of networks and components thereof.
As a result, conventional desktop personal computers are required to have not only an improved information processing capability (including an improved data display performance), but also a new ability to access networks freely and easily through a portable telephone or portable information terminal. Such portable information equipment is expected to function as a platform that provides various applications in which image information is involved in addition to its original functions.
Improvements required of portable information equipment (or terminals) in its fundamental performance include faster transmission speeds for networking, a larger data processing capacity, a better display visibility, lighter weight, and easier handleability and transportability.
Such requirements are applicable also to the flat panel display (such as liquid crystal display device and organic EL device), which is major component of portable information equipment. Improvements sought are reduction in weight and thickness and high-density display (or high definition display).
Attempts have been made to meet such sophisticated and diversified requirements. For example, in the case of a liquid crystal display (LCD), one way to meet requirements for reduction in weight and thickness is to manufacture the LCD panel from a thinner substrate than before. Glass substrates are commonly used in the LCD technology. Therefore, the above-mentioned requirements will be met to some extent by manufacturing the LCD panel from thin glass substrates. Unfortunately, glass suffers the disadvantage of being broken easily by impact due to dropping or external pressure. Therefore, further reduction in thickness would be difficult to achieve from the standpoint of an LCD""s impact resistance and breakage prevention.
Glass sheets now available for LCD panels have a thickness of 1.1 mm, 0.7 mm, 0.5 mm, or 0.4 mm (with 0.7 mm being common) according to xe2x80x9cLiquid Crystal Device Handbookxe2x80x9d (Chapter 4, Section 4.2, page 218, compiled by Japan Society for the Promotion of Science, issued in 1989 by Nikkan Kogyo Shimbunsha). A glass sheet with a thickness of 0.4 mm is difficult to handle in the LCD manufacturing process because of its liability for chipping and breakage, which leads to reduced yields. At present, reduction to about 0.3 mm is considered to be the maximum that can be achieved for display device glass substrates.
Another way under study for improvement in the technical field of an LCD is replacement of glass sheets by plastics sheets, as disclosed in Japanese Patent Laid-open No. 6-175143. Plastics sheets can be made thinner than glass sheets on account of their flexibility (hence providing good crack resistance) and high resistance to dropping impact and external pressure. Plastics sheets have a specific gravity of 1.2-1.4, whereas glass sheets have a specific gravity of 2.3. Therefore, an LCD with a substrate made of a plastic sheet is lighter and thinner than that with a substrate made of a glass sheet.
Unfortunately, plastics sheets usually have a lower transmission for visible light and a higher rate of gas permeability than glass sheets. The latter property poses a problem with foaming in liquid crystal inside the panel.
Plastics sheets with good gas barrier properties should necessarily be thick, and this means that such plastics sheets have a poor light transmission, giving rise to a dark display. Therefore, the resulting LCD based on use of a plastics sheet is inferior in visibility to the conventional LCD based on use of a glass sheet.
In addition, plastics sheets are inferior in heat resistance to glass sheets. At high temperatures, they are subject to discoloration (decrease in light transmission) and deformation (such as bending and warpage). Therefore, production of an LCD with a plastics sheet should be carried out at low temperatures. This makes it necessary to develop new materials usable at low temperatures, such as the sealing agent to bond together paired substrates, with a liquid crystal interposed between them, and an alignment film to align the liquid crystal.
Moreover, a plastics sheet suffers another disadvantage in that it is difficult to form an electrode film thereon from low-resistance ITO (indium-tin oxide) at high temperatures. ITO varies in resistance or conductivity depending on its film-forming temperature. Thus, the disadvantage of an LCD based on use of a plastics sheet is that finely patterned ITO electrodes have a high resistance, which is detrimental to a high definition display.
The conventional plastics sheet does not withstand heat encountered in the process of producing TFTs (thin film transistors) necessary for a high-quality LCD of the active matrix drive type. Thus, it is difficult to form TFTs on a plastics sheet, and hence it is difficult to realize a high-quality display by means of an active matrix drive so long as the LCD is formed with a substrate made of a plastics sheet.
Thus, an LCD formed with a plastics sheet is not comparable to that formed with a glass sheet in producing a high definition display. Thus, it will not be able to display moving pictures.
A third improvement in the technical field of the LCD is to form the display device from a laminate substrate consisting of a pair of glass sheets and a plastics sheet held between them, as disclosed in Japanese Patent Laid-open Nos. 7-43696, 7-49486, and 7-287218. A conventional three-layered laminate substrate used for LCD panels is shown in section in FIG. 1. It consists of a pair of glass sheets 101 and 102 and a soft plastics sheet 103 held between them.
The advantage of the laminate substrate is that the plastics sheet has improved heat resistance owing to the presence of the outer glass sheets. On the other hand, the plastics sheet is usually made of polyvinyl butyral (which is comparatively soft), as disclosed in Japanese Patent Laid-open No. 7-43696, so that the plastics sheet produces no stress in the glass sheets laminated onto both sides thereof.
If an extremely thin plastics sheet (100 xcexcm or so) is used to reduce the total thickness of the substrate, it produces the effect of preventing the glass sheet from shattering when the substrate is broken, but it will not produce the effect of improving impact resistance or preventing the glass sheet from being broken.
It is understood from the foregoing that the conventional technology still has problems to be solved and that there is room for improvement before it is applied to the current flat panel display (LCD and organic EL device).
In order to realize a flat panel display (LCD and organic EL device) with improved performance (including light weight, small thickness, and high definition display), which will be necessary for moving pictures in the future, it is necessary to develop a new technology which fully utilizes the features of a glass sheet and a plastics sheet, but eliminates their disadvantages.
More specifically, the flat panel display according to the new technology should have high heat resistance (ascribed to glass) and light weight and small thickness (ascribed to plastics) and better impact resistance than glass.
It is an object of the present invention to provide a new display device substrate which meets the requirements for reduction in weight and thickness and improvement in gas barrier properties, heat resistance, and impact resistance.
It is another object of the present invention to provide a new display device substrate having a laminate structure consisting of glass sheets and a plastics sheet, such that the glass sheets are more resistant to breaking than before or are equivalent to a 0.3 mm thick glass sheet in impact resistance.
It is another object of the present invention to provide a display device, such as LCD and organic EL device, which is light in weight and small in thickness and is superior in impact resistance and display quality.
The present invention is directed to an improved display device substrate which is composed of a pair of glass sheets facing each other and a layer of plastics material interposed between the glass sheets, wherein the improvement comprises glass sheets having an internal compressive strain.
According to an embodiment of the present invention, the glass sheets have an internal compressive strain ascribed to the layer of plastics material interposed between them.
According to an embodiment of the present invention, the layer of plastics material is that of a thermosetting resin excluding polyurethane.
According to an embodiment of the present invention, the layer of plastics material is that of epoxy resin.
According to an embodiment of the present invention, the layer of plastics material is that of inorganic-organic hybrid material.
According to an embodiment of the present invention, the layer of plastics material is that of epoxy-silicone-based inorganic-organic hybrid material.
According to an embodiment of the present invention, the layer of plastics material is that of epoxy-silicone-based inorganic-organic hybrid material synthesized from an epoxy resin and an organosilicon compound.
According to an embodiment of the present invention, the layer of plastics material is that of inorganic-organic hybrid material synthesized from an epoxy-type organosilicon alkoxide represented by the chemical formula (1) below. 
(where R and Rxe2x80x2 each denote an organic group.)
According to an embodiment of the present invention, the layer of plastics material is that of inorganic-organic hybrid material synthesized from any of epoxy resin of glycidyl ether type composed mainly of a phenolic compound, such as bisphenol-A, bisphenol-F, tetrabromobisphenol-A, tetraphenylolethane, phenol-novolak, and o-cresol-novolak; epoxy resin of glycidyl ether type composed mainly of an alcoholic compound such as polypropylene glycol and hydrogenated bisphenol-A; epoxy resin of glycidyl ester type composed mainly of hexahydrophthalic anhydride or dimmer acid; epoxy resin of glycidyl amine type composed mainly of diaminophenylmethane, isocyanuric acid, or hydantoin; epoxy resin of mixed type composed mainly of p-aminophenol or p-oxybenzoic acid; and epoxy resin composed mainly of an ester represented by the chemical formula (2) below. 
According to an embodiment of the present invention, the layer of plastics material contains a silicon component (in terms of SiO2) in an amount more than 0 wt % and less than 30 wt %.
According to an embodiment of the present invention, the layer of plastics material contains a silicon component (in terms of SiO2) in an amount more than 4 wt % and less than 15 wt %.
According to an embodiment of the present invention, the glass sheets have an internal compressive strain no less than 1.9xc3x9710xe2x88x924.
According to an embodiment of the present invention, the display device substrate has a thickness no larger than 0.3 mm.
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (1) below.
|{(xcex1gxe2x88x92xcex1r)xc3x97xcex94Txc3x97(Erxc3x97hr)}/{(Erxc3x97hr)+(Egxc3x97hg)}|xe2x89xa71.9xc3x9710xe2x88x924xe2x80x83xe2x80x83(1)
(where xcex94T denotes a difference between the operating temperature of the display device substrate and the glass transition point (Tg) of the plastics material or the maximum temperature to be reached by the plastics material during its curing or molding if the latter is lower than the former.)
xcex1g=coefficient of linear expansion of glass used
xcex1r=coefficient of linear expansion of plastics material
Eg=elastic modulus of glass
Er=elastic modulus of plastics material
hg=total thickness of glass sheets
hr=thickness of plastics material
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (2) below.
{xcex1rxc3x97xcex94Txc3x97(Erxc3x97hr)}/{Egxc3x97hg}xe2x89xa71.9xc3x9710xe2x88x924xe2x80x83xe2x80x83(2)
According to an embodiment of the present invention, the display device substrate satisfies the mathematical expression (2) and the glass sheets have a total thickness no smaller than 60 xcexcm.
According to an embodiment of the present invention, the display device substrate satisfies the mathematical expression (2) and the glass sheets have a total thickness no smaller than 100 xcexcm.
According to an embodiment of the present invention, the display device substrate satisfies the mathematical expression (2) and the glass sheets have a total thickness no smaller than 140 xcexcm.
According to an embodiment of the present invention, the display device substrate satisfies the mathematical expression (3).
{xcex1rxc3x97xcex94Txc3x97(Erxc3x97hr)}xe2x89xa72800 Paxc2x7m (Pascal-meter)xe2x80x83xe2x80x83(3)
According to an embodiment of the present invention, the display device substrate satisfies the mathematical expression (4).
(xcex1rxc3x97xcex94Txc3x97hr)xe2x89xa71.4xc3x9710xe2x88x926 mxe2x80x83xe2x80x83(4)
According to an embodiment of the present invention, the display device substrate satisfies the mathematical expression (5) and the glass sheets have a total thickness no smaller than 150 xcexcm.
{xcex1rxc3x97xcex94Txc3x97(Erxc3x97hr)}2100 Paxc2x7mxe2x80x83xe2x80x83(5)
According to an embodiment of the present invention, the display device substrate satisfies the mathematical expression (6) and the glass sheets have a total thickness no smaller than 100 xcexcm.
{xcex1rxc3x97xcex94Txc3x97(Erxc3x97hr)}xe2x89xa71400 Paxc2x7mxe2x80x83xe2x80x83(6)
According to an embodiment of the present invention, the maximum temperature to be reached by the plastics material during its curing or molding is lower than its glass transition point (Tg) and xcex94T is a difference between the operating temperature of the display device substrate and the maximum temperature to be reached by the plastics material during its curing or molding.
According to an embodiment of the present invention, the glass sheets have an internal compressive strain no smaller than 3.4xc3x9710xe2x88x924.
According to an embodiment of the present invention, the display device substrate has a thickness no larger than 0.3 mm.
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (7).
|{(xcex1gxe2x88x92xcex1r)xc3x97xcex94Txc3x97(Erxc3x97hr)}/{(Erxc3x97hr)+(Egxc3x97hg)}|xe2x89xa73.4xc3x9710xe2x88x924xe2x80x83xe2x80x83(7)
(where xcex94T denotes a difference between the operating temperature of the display device substrate and the glass transition point (Tg) of the plastics material or the maximum temperature to be reached by the plastics material during its curing or molding if the latter is lower than the former.)
xcex1g=coefficient of linear expansion of glass used
xcex1r=coefficient of linear expansion of plastics material
Eg=elastic modulus of glass
Er=elastic modulus of plastics material
hg=total thickness of glass sheets
hr=thickness of plastics material
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (8).
{xcex1rxc3x97xcex94Txc3x97(Erxc3x97hr)}/{Egxc3x97hg}xe2x89xa73.4xc3x9710xe2x88x924xe2x80x83xe2x80x83(8)
According to an embodiment of the present invention, the glass sheets have a total thickness no smaller than 100 xcexcm.
According to an embodiment of the present invention, the glass sheets have a total thickness no smaller than 140 xcexcm.
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (9) and the glass sheets have a total thickness no larger than 140 xcexcm.
{xcex1rxc3x97xcex94Txc3x97(Erxc3x97hr)}xe2x89xa73500 Paxc2x7mxe2x80x83xe2x80x83(9)
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (10) and the glass sheets have a total thickness no larger than 140 xcexcm.
(xcex1rxc3x97xcex94Txc3x97hr)xe2x89xa71.7xc3x9710xe2x88x926 mxe2x80x83xe2x80x83(10)
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (11) and the glass sheets have a total thickness no larger than 100 xcexcm.
{xcex1rxc3x97xcex94Txc3x97(Erxc3x97hr)}xe2x89xa72500 Paxc2x7mxe2x80x83xe2x80x83(b 11)
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (12) and the glass sheets have a total thickness no larger than 100 xcexcm.
(xcex1rxc3x97xcex94Txc3x97hr)xe2x89xa71.2xc3x9710xe2x88x926 mxe2x80x83xe2x80x83(12)
According to an embodiment of the present invention, the maximum temperature to be reached by the plastics material during its curing or molding is lower than its glass transition point (Tg) and xcex94T is a difference between the operating temperature of the display device substrate and the maximum temperature to be reached by the plastics material during its curing or molding.
According to an embodiment of the present invention, the display device substrate has a thickness no larger than 0.2 mm and the glass sheets have an internal compressive strain no smaller than 3.4xc3x9710xe2x88x924.
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (13).
|{(xcex1gxe2x88x92xcex1r)xc3x97xcex94Txc3x97(Erxc3x97hr)}/{(Erxc3x97hr)+(Egxc3x97hg)}|xe2x89xa73.4xc3x9710xe2x88x924xe2x80x83xe2x80x83(13)
(where xcex94T denotes a difference between the operating temperature of the display device substrate and the glass transition point (Tg) of the plastics material or the maximum temperature to be reached by the plastics material during its curing or molding if the latter is lower than the former.)
xcex1g=coefficient of linear expansion of glass used
xcex1r=coefficient of linear expansion of plastics material
Eg=elastic modulus of glass
Er=elastic modulus of plastics material
hg=total thickness of glass sheets
hr=thickness of plastics material
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (14).
{xcex1rxc3x97xcex94Txc3x97(Erxc3x97hr)}/{Egxc3x97hg}xe2x89xa73.4xc3x9710xe2x88x924xe2x80x83xe2x80x83(14)
According to an embodiment of the present invention, the glass sheets have a total thickness no smaller than 100 xcexcm.
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (15) and the glass sheets have a total thickness no larger than 100 xcexcm.
{xcex1rxc3x97xcex94Txc3x97(Erxc3x97hr)}xe2x89xa72500 Paxc2x7mxe2x80x83xe2x80x83(15)
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (16) and the glass sheets have a total thickness no larger than 100 xcexcm.
(xcex1rxe2x88x92xcex94Txc3x97hr)xe2x89xa71.2xc3x9710xe2x88x926 mxe2x80x83xe2x80x83(16)
According to an embodiment of the present invention, the maximum temperature to be reached by the plastics material during its curing or molding is lower than its glass transition point (Tg) and xcex94T is a difference between the operating temperature of the display device substrate and the maximum temperature to be reached by the plastics material during its curing or molding.
According to an embodiment of the present invention, the glass sheets have an internal compressive strain no smaller than 5.0xc3x9710xe2x88x924.
According to an embodiment of the present invention, the display device substrate has a thickness no larger than 0.3 mm.
According to an embodiment of the present invention, the display device substrate satisfies the relation represented by the mathematical expression (17).
|{(xcex1gxe2x88x92xcex1r)xc3x97xcex94Txc3x97(Erxc3x97hr)}/{(Erxc3x97hr)+(Egxc3x97hg)}|xe2x89xa75.0xc3x9710xe2x88x924xe2x80x83xe2x80x83(17)
(where xcex94T denotes a difference between the operating temperature of the display device substrate and the glass transition point (Tg) of the plastics material or the maximum temperature to be reached by the plastics material during its curing or molding if the latter is lower than the former.)
xcex1g=coefficient of linear expansion of glass used
xcex1r=coefficient of linear expansion of plastics material
Eg=elastic modulus of glass
Er=elastic modulus of plastics material
hg=total thickness of glass sheets
hr=thickness of plastics material
According to an embodiment of the present invention, the glass sheets have a total thickness no smaller than 100 xcexcm.
According to an embodiment of the present invention, the glass sheets have a total thickness no smaller than 140 xcexcm.
The present invention is directed also to a display device which is formed with at least one piece of the display device substrate defined above.